Pane having an electric heating layer

ABSTRACT

A pane having an electric heating layer is described, including: a first pane having a surface; at least one electric heating layer that is applied to at least part of the surface and has at least one uncoated zone; at least two busbars, provided for connection to a voltage source, which are connected to the electric heating layer such that a current path for a heating current is formed between the busbars; and n separating lines which electrically subdivide the electric layer into m segments. The segments are arranged in the form of strips around the uncoated zone such that the current path for the heating current is at least partially guided around the uncoated zone and the segments have equal width and the sum of widths of segments is equal to the width of the electric heating layer.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a U.S. Continuation Application of U.S. Ser.No. 14/653,847 filed on Jun. 18, 2015, which in turn, claims priority toU.S. national stage of International Patent ApplicationPCT/EP2013/073231 filed internationally on Nov. 7, 2013, which in turn,claims priority to European Patent Application No. 12198371.2 filed onDec. 20, 2012, all of which are incorporated herein by reference intheir entirety.

BACKGROUND

The invention relates to a pane having an electric heating layer, amethod for its production, and its use.

The field of vision of a motor vehicle window, in particular awindshield, must be kept free of ice and condensation. In the case ofmotor vehicles with an internal combustion engine, a stream of airheated by engine heat can, for example, be directed to the windows.

Alternatively, the window can have an electrical heating function. Thus,composite glass panes that have an electric heating layer made of atransparent, electrically conductive coating on an interior-side surfaceof one of the individual panes are known. Using an external voltagesource, an electric current that heats the coating and, with it, thepane can be conducted through the electrically conductive coating.W02012/052315 A1 discloses, for example, such a heatable, electricallyconductive coating based on metal.

The electrical contacting of the electric heating layer is typicallydone via busbars, as is known from US 2007/0020465 A1. The busbars aremade, for example, from a printed and fired silver paste. The busbarstypically run along the upper and lower edge of the pane. The busbarscollect the current that flows through the electric heating layer andconduct it to external feed lines that are connected to a voltagesource.

The patterning of the electric heating layer by separating lines orseparating zones for the formation of a usually winding current path isknown from the industrial series production of panes having an electricheating layer. This has the advantage that the electrical resistance canbe increased and the current path can be contacted by relatively smallconnection electrodes. In the patent literature, such a heatable pane isdescribed, for example, in DE 19860870 A1.

Panes having an electric heating layer shield relatively stronglyagainst electromagnetic radiation such that, in particular in motorvehicles with a heatable windshield, radio data traffic can besignificantly impaired. Heatable windshields are, consequently,frequently provided with uncoated or coating-free zones (“communicationwindows”), which are readily permeable at least for specific ranges ofthe electromagnetic spectrum. In this manner, trouble-free data trafficis enabled. The uncoated zones, on which electronic devices, such assensors, cameras, and the like, are situated, are often arranged in thevicinity of the upper edge of the pane where they can be readilyconcealed by the upper masking strip.

However, uncoated zones negatively affect the electrical properties ofthe heating layer, which at least locally affects the current densitydistribution of the heating current flowing through the heating layer.In fact, they cause a highly inhomogeneous heating power distribution,with the heating power significantly reduced below and in the vicinityof the uncoated zones. On the other hand, spots with a particularly highcurrent density develop, in which the heating power is greatlyincreased. As a consequence, very high local pane temperatures, whichconstitute a risk of burns, can occur and impose high thermal stresseson the panes. In addition, this can cause loosening of bonding sites ofattachments.

SUMMARY OF INVENTION

The object of the present invention consists in providing an improvedpane having an uncoated zone and at least approximately uniform heatingpower distribution, which is simple and economical to produce.

The object of the present invention is accomplished according to theinvention by a pane having an electric heating layer in accordance withclaim 1. Preferred embodiments emerge from the subclaims.

The pane according to the invention having an electric heating layercomprises at least the following features:

-   -   a first pane with a surface,    -   at least one electric heating layer made of an electrically        conductive coating to heat the first pane, whereby the electric        heating layer is arranged on at least a part of the surface and        includes at least one uncoated zone,    -   at least two busbars provided for connection to a voltage        source, which are connected to the electric heating layer such        that a current path for a heating current is formed between the        busbars, and    -   n separating lines, which electrically subdivide the electric        heating layer into m segments, where n is an integer ≥1 and        m=n+1,

wherein the segments are arranged in strip form around the uncoated zonesuch that the current path for the heating current is guided at leastpartially around the uncoated zone and the width b of the segments isequal and the sum of the widths b of the segments is equal to the widthB of the electric heating layer.

This means that the segments are arranged at least partially in stripform around the uncoated zone such that the current path for the heatingcurrent is at least partially guided around the uncoated zone and thewidth b of each segment equals the m^(th) part of the width B of theelectric heating layer along a line parallel to the busbars.

The busbars are preferably arranged parallel or approximately parallelto each other since this results in homogeneous current densitydistribution over the electric heating layer. When the busbars are notarranged parallel to each other, for example, in order to heat aspecific region of the electric heating layer more, the line fordetermination of the width of the electric heating layer is understoodto be along an equipotential line of an electric heating layer with nouncoated zone.

The electric heating layer includes at least one uncoated zone. Thismeans that the uncoated zone is completely or partially surrounded bythe electric heating layer. The uncoated zone can, in particular, borderan edge region of the electric heating layer or be extended via anuncoated strip beyond the edge region of the electric heating layer.

The width b of the segments depends on the width B of the electricheating layer in a respective line parallel to the busbars. The width bof the segments is calculated by dividing the width B of the electricheating layer by the number of segments. When the electric heating layerhas one or a plurality of uncoated zones, the width B of the electricheating layer is determined without the width of the uncoated zone.

In an advantageous embodiment of the invention, the width b of theindividual segments can deviate as much as 10% from each other, i.e.,from the quotient of the width B of the heating layer divided by thenumber of segments. Preferably, the deviation is ≤5%, particularlypreferably ≤2%.

According to the invention, the electric heating layer is subdivided byseparating lines into individual segments, each of which guides thecurrent path of the heating current around the uncoated zone. Theheating current is, in particular, also guided into the regions aboveand below the uncoated zone. Here, “above” and “below” mean relative tothe direction of the shortest connection lines between the busbars of apane with no uncoated zone.

The homogeneity of the heating power distribution increases with thenumber of separating lines and individual segments that guide theheating current. In an advantageous embodiment, the electric heatinglayer has at least n=3 separating lines and preferably n=7 to 25separating lines. The separating lines preferably form segments that arearranged at least partially in strip form around the uncoated zone.

Panes according to the invention with a separating line number from 7 to25 lines have particularly good homogeneity of heating powerdistribution with, at the same time, economical cost and timeexpenditures due to the introduction of the separating lines.

In another advantageous embodiment of the pane according to theinvention, the width d of the separating line is from 30 μm to 200 μmand preferably from 70 μm to 140 μm.

This has the particular advantage that separating lines with such asmall width negatively affect vision through the pane only very littleor not at all.

In another advantageous embodiment of the pane according to theinvention, the area of the uncoated zone is from 0.5 dm² to 15 dm² andpreferably from 2 dm² to 8 dm².

Panes according to the prior art without separating lines according tothe invention and with such large uncoated zones have particularlyinhomogeneous heating power distributions and can be only inadequatelyfreed of ice, snow, and condensation under poor weather conditions.Through the use of the separating lines according to the invention, aparticularly high improvement of the heating characteristics of the panecan be obtained with such a large uncoated zone.

The busbars are preferably arranged along the side edge on theelectrically conductive coating of the electric heating layer. Thelength of the busbar is typically substantially equal to the length ofthe side edge of the electrically conductive coating, but can also beslightly larger or smaller. Also, more than two busbars can be arrangedon the electrically conductive coating, preferably in the edge regionalong two opposite side edges of the electrically conductive coating.Even more than two busbars can be arranged on the electric heatinglayer, for example, to form two or more independent heating fields in anelectrically heatable coating or when the busbar is interrupted ordisplaced by one or more uncoated zones. The teaching according to theinvention then applies for at least one and preferably for each of theindependent heating fields.

In an advantageous embodiment, the busbar according to the invention isimplemented as a printed and fired conductive structure. The printedbusbar preferably contains at least one metal, a metal alloy, a metalcompound, and/or carbon, particularly preferably a noble metal, inparticular, silver. The printing paste preferably contains metallicparticles, metal particles, and/or carbon and, in particular, noblemetal particles such as silver particles. Electrical conductivity ispreferably obtained by means of the electrically conductive particles.The particles can be situated in an organic and/or an inorganic matrixsuch as pastes or inks, preferably as printing paste with glass frits.

The width of the first and second busbar is preferably from 2 mm to 30mm, particularly preferably from 4 mm to 20 mm, and in particular from10 mm to 20 mm. Thinner busbars result in an excessively high electricalresistance and thus in an excessively high heating of the busbar duringoperation. Moreover, thinner busbars are difficult to produce usingprinting techniques such as screen printing. Thicker busbars require anundesirably high use of material. Moreover, they result in anexcessively large and unaesthetic reduction in the region of the panethat can be seen through. The length of the busbar is governed by thedimension of the electric heating layer. In the case of a busbar that istypically implemented in the form of a strip, the longer of itsdimensions is referred to as length and the less long of its dimensionsis referred to as width. The third busbars or additional busbars can beimplemented even thinner, preferably from 0.6 mm to 5 mm.

The layer thickness of the printed busbar is preferably from 5 μm to 40μm, particularly preferably from 8 μm to 20 μm, and most particularlypreferably from 8 μm to 12 μm.

Printed busbars with these thicknesses are technically simple to realizeand have an advantageous current-carrying capacity.

The specific resistance ρ_(a) of the busbars is preferably from 0.8μohm·cm to 7.0 μohm·cm and particularly preferably from 1.0 μohm·cm to2.5 μohm·cm. Busbars with specific resistances in this range aretechnically simple to realize and have an advantageous current-carryingcapacity.

Alternatively, however, the busbar can also be implemented as a strip ofan electrically conductive foil. In that case, the busbar contains, forexample, at least aluminum, copper, tinned copper, gold, silver, zinc,tungsten, and/or tin or alloys thereof. The strip preferably has athickness from 10 μm to 500 μm, particularly preferably from 30 μm to300 μm. Busbars made of electrically conductive foils with thesethicknesses are technically simple to realize and have an advantageouscurrent-carrying capacity. The strip can be electrically conductivelyconnected to the electrically conductive structure, for example, via asoldering compound, via an electrically conductive adhesive, or bydirect placement.

The pane according to the invention includes a first pane, on which anelectric heating layer is arranged. Depending on the type of theelectric heating layer, it is advantageous to protect the heating layerwith a protective layer, for example, a lacquer, a polymer film, and/ora second pane.

In an advantageous embodiment of the pane according to the invention,the surface of the first pane, on which the electrically conductivecoating is arranged, is areally bonded to a second pane via athermoplastic intermediate layer.

Basically, all electrically insulating substrates that are thermally andchemically stable as well as dimensionally stable under the conditionsof production and use of the pane according to the invention aresuitable as the first and, optionally, the second pane.

The first pane and/or the second pane preferably contain glass,particularly preferably flat glass, float glass, quartz glass,borosilicate glass, soda lime glass, or clear plastics, preferably rigidclear plastics, in particular polyethylene, polypropylene,polycarbonate, polymethyl methacrylate, polystyrene, polyamide,polyester, polyvinyl chloride, and/or mixtures thereof. The first paneand/or the second pane are preferably transparent, in particular for theuse of the pane as a windshield or rear window of a motor vehicle orother uses in which high light transmittance is desired. In the contextof the invention, “transparent” means a pane that has transmittance ofmore than 70% in the visible spectral range. For panes, that are notsituated in the traffic-relevant field of vision of the driver, forexample, for roof panes, the transmittance can, however, also be muchlower, for example, more than 5%.

The thickness of the pane can vary widely and thus be ideally adapted tothe requirements of the individual case. Preferably, panes with thestandard thicknesses from 1.0 mm to 25 mm, preferably from 1.4 mm to 2.5mm are used for motor vehicle glass and preferably from 4 mm to 25 mmfor furniture, devices, and buildings, in particular for electricheaters. The size of the pane can vary widely and is determined by thesize of the use according to the invention. The first pane and,optionally, the second pane have, for example, in the automobile sectorand the architectural sector, customary areas from 200 cm² all the wayto 20 m².

The pane can have any three-dimensional shape. Preferably, thethree-dimensional shape has no shadow zones such that it can, forexample, be coated by cathode sputtering. Preferably, the substrates areplanar or slightly or greatly curved in one or a plurality of spatialdirections. In particular, planar substrates are used. The panes can becolorless or tinted.

Multiple panes are bonded to each other by at least one intermediatelayer. The intermediate layer preferably contains at least onethermoplastic polymer, preferably polyvinyl butyral (PVB), ethylenevinyl acetate (EVA), and/or polyethylene terephthalate (PET). Thethermoplastic intermediate layer can, however, also contain, forexample, polyurethane (PU), polypropylene (PP), polyacrylate,polyethylene (PE), polycarbonate (PC), polymethyl methacrylate,polyvinyl chloride, polyacetate resin, casting resins, acrylates,fluorinated ethylene propylenes, polyvinyl fluoride, and/or ethylenetetrafluoroethylene, or copolymers or mixtures thereof. Thethermoplastic intermediate layer can be formed by one or even aplurality of thermoplastic films arranged one over another, with thethickness of a thermoplastic film being preferably from 0.25 mm to 1 mm,typically 0.38 mm or 0.76 mm.

In a composite pane according to the invention made of a first pane, anintermediate layer, and a second pane, the electric heating layer can beapplied directly on the first pane or on a carrier film or on theintermediate layer itself. The first pane and the second pane have ineach case an interior-side surface and an exterior-side surface.

The interior-side surfaces of the first and of the second pane face eachother and are bonded to each other via the thermoplastic intermediatelayer. The exterior-side surfaces of the first and of the second paneface away from each other and away from the thermoplastic intermediatelayer. The electric heating layer is preferably applied on theinterior-side surface of the first pane. Of course, another electricallyconductive coating can be applied on the interior-side surface of thesecond pane. The exterior-side surfaces of the panes can also havecoatings. The terms “first pane” and “second pane” are selected todistinguish between the two panes in a composite pane according to theinvention. No statement concerning the geometric arrangement isassociated with the terms. If, for example, the pane according to theinvention is provided in an opening, for example, of a motor vehicle ora building, to separate the interior from the external environment, thefirst pane can face the interior or the external environment.

The electric heating layer includes electrically conductive coating andpreferably a transparent, electrically conductive coating. Here,“transparent” means permeable to electromagnetic radiation, preferablyelectromagnetic radiation of a wavelength from 300 nm to 1.300 nm and inparticular to visible light.

Electrically conductive coatings according to the invention are known,for example, from DE 20 2008 017 611 U1, EP 0 847 965 B1, orW02012/052315 A1. They typically contain one or more, for example, two,three, or four electrically conductive, functional layers. Thefunctional layers preferably contain at least one metal, for example,silver, gold, copper, nickel, and/or chromium or a metal alloy. Thefunctional layers particularly preferably contain at least 90 wt.-% ofthe metal, in particular at least 99.9 wt.-% of the metal. Thefunctional layers can be made of the metal or the metal alloy. Thefunctional layers particularly preferably contain silver or asilver-containing alloy. Such functional layers have a particularlyadvantageous electrical conductivity with, at the same time, hightransmittance in the visible spectral range. The thickness of afunctional layer is preferably from 5 nm to 50 nm, particularlypreferably from 8 nm to 25 nm. In this range for the thickness of thefunctional layer, an advantageously high transmittance in the visiblespectral range and a particularly advantageous electrical conductivityare obtained.

Typically, at least one dielectric layer is arranged, in each case,between two adjacent functional layers of the heatable coating.Preferably, another dielectric layer is arranged below the first and/orabove the last functional layer. A dielectric layer contains at leastone individual layer made of a dielectric material, for example,containing a nitride such as silicon nitride or an oxide such asaluminum oxide. Dielectric layers can, however, also include multipleindividual layers, for example, individual layers of a dielectricmaterial, smoothing layers, matching layers, blocker layers, and/oranti-reflection layers. The thickness of a dielectric layer is, forexample, from 10 nm to 200 nm.

This layer structure is generally obtained through a sequence ofdeposition procedures that are performed using a vacuum method such asmagnetically enhanced cathodic sputtering.

Other suitable electrically conductive coatings preferably containindium tin oxide (ITO), fluorine-doped tin oxide (SnO2:F), oraluminum-doped zinc oxide (ZnO:Al).

The electrically conductive coating can, in principle, be any coatingthat can be electrically contacted. If the pane according to theinvention is intended to enable vision through it, as is the case, forexample, with panes in the window area, the electrically conductivecoating is preferably transparent. In an advantageous embodiment, theelectrically conductive coating is a layer or a layer structure of aplurality of individual layers with a total thickness less than or equalto 2 μm, particularly preferably less than or equal to 1 μm.

An advantageous electric heating layer according to the invention has asheet resistance from 0.4 ohm/square to 10 ohm/square. In a particularlypreferred embodiment, the electric heating layer according to theinvention has a sheet resistance from 0.5 ohm/square to 1 ohm/square.Coatings with such sheet resistances are particularly well-suited forthe heating of motor vehicle window panes at typical onboard voltagesfrom 12 V to 48 volts or in electric motor vehicles with typical onboardvoltages of as much as 500 V.

The electric heating layer can extend over the entire surface of thefirst pane. Alternatively, the electric heating layer can also extendover only part of the surface of the first pane. The electric heatinglayer preferably extends over at least 50%, particularly preferably overat least 70%, and most particularly preferably over at least 90% of theinterior-side surface of the first pane. The electric heating layer canhave one or a plurality of uncoated zones. These zones can be permeablefor electromagnetic radiation and are known, for example, as datatransmission windows or communication windows.

In an advantageous embodiment of the pane according to the invention asa composite pane, the interior-side surface of the first pane has acircumferential edge region with a width from 2 mm to 50 mm, preferablyfrom 5 mm to 20 mm, that is not provided with the electricallyconductive coating of the electric heating layer. Then, the electricallyconductive coating has no contact with the atmosphere and is, in theinterior of the pane, advantageously protected by the thermoplasticintermediate layer against damage and corrosion.

The electrical feed line is preferably implemented as a flexible foilconductor (flat conductor, ribbon cable). This means an electricalconductor whose width is significantly greater than its thickness. Sucha foil conductor is, for example, a strip or band containing or made ofcopper, tinned copper, aluminum, silver, gold, or alloys thereof. Thefoil conductor has, for example, a width from 2 mm to 16 mm and athickness from 0.03 mm to 0.1 mm. The foil conductor can have aninsulating, preferably polymeric sheath, for example, polyimide-based.Foil conductors that are suitable for the contacting of electricallyconductive coatings in panes have only a total thickness of, forexample, 0.3 mm. Such thin foil conductors can be embedded withoutdifficulty in the thermoplastic intermediate layer between theindividual panes. A plurality of conductive layers electrically isolatedfrom each other can be situated in a foil conductor band.

Alternatively, thin metal wires can also be used as an electrical feedline. The metal wires contain, in particular, copper, tungsten, gold,silver, or aluminum or alloys of at least two of these metals. Thealloys can also contain molybdenum, rhenium, osmium, iridium, palladium,or platinum.

In an advantageous embodiment of the invention, the electrical feed lineis connected to a contact strip, for example, by means of a solderingcompound or an electrically conductive adhesive. The contact strip isthen connected to the busbar. The contact strip advantageously increasesthe current-carrying capacity of the busbar. Also, undesirable heatingof the contact point between the busbar and the feed line can beprevented by the contact strip. In addition, the contact stripsimplifies the electrical contacting of the busbar by the electricalfeed line since the feed line does not have to be connected, forexample, soldered, to the already applied busbar.

The contact strip preferably contains at least one metal, particularlypreferably copper, tinned copper, silver, gold, aluminum, zinc,tungsten, and/or tin. This is particularly advantageous with regard tothe electrical conductivity of the contact strip. The contact strip canalso include alloys which preferably contain one or a plurality of theelements mentioned and, optionally, other elements, for example, brassor bronze.

The contact strip is preferably implemented as a strip of a thin,electrically conductive foil. The thickness of the contact strip ispreferably from 10 μm to 500 μm, particularly preferably from 15 μm to200 μm, most particularly preferably from 50 μm to 100 μm. Foils withthese thicknesses are technically simple to produce and readilyavailable and also have an advantageously low electrical resistance.

The length of the contact strip is preferably from 10 mm to 400 mm,particularly preferably from 10 mm to 100 mm and, in particular, 20 mmto 60 mm. This is particularly advantageous with regard to goodhandleability of the contact strip as well as an adequately largecontact area for the electrical contacting between the busbar and thecontact strip.

The width of the contact strip is preferably from 2 mm to 40 mm,particularly preferably from 5 mm to 30 mm. This is particularlyadvantageous with regard to the contact area between the contact stripand the busbar and simple connection of the contact strip to theelectrical feed line. The terms “length” and “width” of the contactstrip refer in each case to the dimension in the same directionindicated by “length” or “width” of the busbar.

In a preferred embodiment, the contact strip is in direct contact withthe busbar over its entire surface. For this, a contact strip is placedon the busbar. The particular advantage resides in simple production ofthe pane and the use of the entire surface of the contact strip as thecontact surface.

The contact strip can simply be placed on the busbar and is durablystably fixed in the intended position inside the laminated pane.

The invention further comprises a method for producing a pane withelectrical contacting, comprising at least:

(a) application of an electric heating layer with an uncoated zone on asurface (III) of a first pane,

(b) application of at least two busbars substantially parallel to eachother provided for connection to a voltage source, which are connectedto the electric heating layer such that a current path for a heatingcurrent is formed between the busbars, and

(c) introduction of n separating lines, which electrically subdivide theelectric heating layer into m segments, where n is an integer ≥1 andm=n+1, wherein the segments are arranged at least partially in stripform around the uncoated zone such that the current path for the heatingcurrent is guided at least partially around the uncoated zone and thewidth b of all segments is equal and the sum of the widths b of thesegments is equal to the width B of the electric heating layer.

When the busbars run parallel or approximately parallel to each other,the width B is advantageously determined along a line parallel to thebusbars. When the electric heating layer has an uncoated zone, the widthB is the sum of the widths of the electric heating layer that surroundthe uncoated zone, in other words, in the determination of the width B,the width of the uncoated zone along the parallel line is not taken intoaccount.

The application of the electric heating layer in process step (a) can bedone by methods known per se, preferably by magnetically enhancedcathodic sputtering. This is particularly advantageous with regard tosimple, fast, economical, and uniform coating of the first pane.However, the electric heating layer can also be applied, for example, byvapor deposition, chemical vapor deposition (CVD), plasma enhancedchemical vapor deposition (PECVD), or by wet chemical methods.

The first pane can be subjected to a temperature treatment after processstep (a). The first pane with the electrically conductive coating isheated to a temperature of at least 200° C., preferably at least 300° C.The temperature treatment can serve to increase the transmittance and/orto reduce the sheet resistance of the electric heating layer.

The first pane can be bent after process step (a), typically at atemperature from 500 ° C. to 700 ° C. Since it is technically simpler tocoat a flat pane, this procedure is advantageous if the first pane is tobe bent. However, alternatively, the first pane can also be bent beforeprocess step (a), for example, if the electric heating layer is unsuitedto withstand a bending process without damage.

The application of the busbar in process step (b) is preferably done byprinting and firing an electrically conductive paste in a screenprinting process or in an inkjet process. Alternatively, the busbar canbe applied, preferably placed, soldered, or glued, on the electricallyconductive coating as a strip of an electrically conductive foil.

In screen printing methods, the lateral shaping is done by masking themesh through which the printing paste with the metal particles ispressed. By means of appropriate shaping of the masking, the width b ofthe busbar, for example, can be predefined and varied in a particularlysimple manner.

The decoating of individual separating lines in the electricallyconductive coating is done preferably using a laser beam. Methods forpatterning thin metal foils are known, for example, from EP 2 200 097 A1or EP 2 139 049 A1. The width of the decoating is preferably 10 μm to1000 μm, particularly preferably 30 μm to 200 μm, and in particular 70μm to 140 μm. In this range, a particularly clean and residue-freedecoating takes place using the laser beam. The decoating using a laserbeam is particularly advantageous since the decorated lines areoptically very inconspicuous and the appearance and the vision throughthe pane are negatively affected only slightly. The decoating of a linewith a width that is wider than the width of a laser cut is done byrepeated runs along the line with a laser beam. Consequently, theduration and costs of the process increase with increasing line width.Alternatively, the decoating can be done by mechanical ablation as wellas by chemical or physical etching.

An advantageous improvement of the method according to the inventionincludes at least the following additional steps:

(d) arranging a thermoplastic intermediate layer on the coated surfaceof the first pane and arranging a second pane on the thermoplasticintermediate layer, and

(e) bonding the first pane and the second pane via the thermoplasticintermediate layer.

In process step (d), the first pane is arranged such that the one of itssurfaces which is provided with the electrically conductive coatingfaces the thermoplastic intermediate layer. The surface thus becomes theinterior-side surface of the first pane.

The thermoplastic intermediate layer can be formed by one singlethermoplastic film or by two or more thermoplastic films that arearranged areally one over another.

The bonding of the first and second pane in process step (e) ispreferably done under the action of heat, vacuum, and/or pressure.Methods known per se can be used for producing a pane.

For example, so-called autoclave methods can be performed at an elevatedpressure of roughly 10 bar to 15 bar and temperatures from 130° C. to145° C. over roughly 2 hours. Vacuum bag or vacuum ring methods knownper se operate, for example, at roughly 200 mbar and 80° C. to 110° C.The first pane, the thermoplastic intermediate layer, and the secondpane can also be pressed in a calender between at least one pair ofrollers to form a pane. Systems of this type are known for producingpanes and normally have at least one heating tunnel upstream before apressing facility. The temperature during the pressing procedure is, forexample, from 40° C. to 150° C.

Combinations of calendering and autoclaving methods have provenespecially effective in practice. Alternatively, vacuum laminators canbe used. These consist of one or a plurality of heatable and evacuablechambers in which the first pane and the second pane are laminatedwithin, for example, roughly 60 minutes at reduced pressures from 0.01mbar to 800 mbar and temperatures from 80° C. to 170° C.

The invention further includes the use of the pane according to theinvention with electrical contacting in buildings, in particular in theaccess area, window area, roof area, or façade area, as a built-incomponent in furniture and devices, in means of transportation fortravel on land, in the air, or on water, in particular in trains, boats,and motor vehicles, for example, as a windshield, rear window, sidewindow, and/or roof pane.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in detail in the following with reference todrawings and exemplary embodiments. The drawings are a schematicrepresentation and not true to scale. The drawings in no way restrictthe invention.

They depict:

FIG. 1 a plan view of an embodiment of the pane according to theinvention having an electric heating layer,

FIG. 2 a plan view of a pane according to the prior art,

FIG. 3 a plan view of another embodiment of the pane according to theinvention,

FIG. 4 a plan view of another embodiment of the pane according to theinvention,

FIG. 5 a plan view of another embodiment of the pane according to theinvention, and

FIG. 6 a detailed flowchart of an embodiment of the method according tothe invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 depicts a plan view of an exemplary embodiment of a pane 100according to the invention having an electric heating layer 3. The pane100 comprises a first pane 1 and is made, for example, of soda limeglass. An electric heating layer 3 made of an electrically conductivecoating is applied on a surface III of the first pane 1. The electricheating layer 3 is a layer system that contains, for example, threeelectrically conductive silver layers that are separated from each otherby dielectric layers. When a current flows through the electric heatinglayer 3, it is heated due to its electrical resistance and Joule heatdevelopment. The electric heating layer 3 can, consequently, be used foractive heating of the pane 100. The dimensions of the pane 100 are, forexample, 1 m×1 m.

The electric heating layer 3 extends, for example, over the entiresurface III of the first pane 1 minus a circumferential frame-shapeduncoated region with a width of 1 cm, in each case.

For the electrical contacting of the electric heating layer 3, a firstbusbar 5.1 is arranged in the lower edge region and another, secondbusbar 5.2 is arranged in the upper edge region, respectively, on theelectric heating layer 3. The busbars 5.1, 5.2 contain, for example,silver particles and were applied by screen printing and then fired. Thelength of the busbars 5.1, 5.2 corresponds to approximately thedimension of the electric heating layer 3. The two busbars 5.1, 5.2 runapproximately parallel.

When an electric voltage is applied to the busbars 5.1 and 5.2, auniform current flows along current paths 11 through the electricheating layer 3 between the busbars 5.1, 5.2. On each busbar 5.1, 5.2, afeed line 7 that is electrically conductively connected to the busbar5.1, 5.2 is arranged approximately centrally. The busbars 5.1, 5.2 areconnected to a voltage source via the electrical feed lines 7.

An uncoated zone 8 is arranged in the center of the pane 100. Theuncoated zone 8 has no electrically conductive material of the electricheating layer 3. Here, the uncoated zone 8 is, for example, completelysurrounded by the electric heating layer 3. The uncoated zone 8 is, forexample, implemented in the shape of a circle and has a diameter of 10cm.

Here, the electric heating layer 3 has n=3 separating lines 9.1, 9.2,9.3. In the region of the separating lines 9.1, 9.2, 9.3, the electricheating layer 3 is electrically interrupted. The separating lines 9.1,9.2, 9.3 are arranged in strip form around the uncoated zone 8 and formfour segments 10.1, 10.2, 10.3, 10.4 in the electric heating layer 3.The current paths 11 are guided around the uncoated zone 8 by thesegments 10.1, 10.2, 10.3, 10.4 in the electric heating layer 3. Inparticular, the current paths 11 in the segments 10.1, 10.3 are guidedin the immediate vicinity of the uncoated zone 8 into the region 12above and below the uncoated zone 8. In this region, only a smallheating power would be obtained in an electric heating layer 3 accordingto the prior art without separating lines (cf. FIG. 2).

The separating lines 9.1, 9.2, 9.3 have a width of, for example, only100 μm and are, for example, introduced into the electric heating layer3 by laser patterning. Separating lines 9.1, 9.2, 9.3 with such a smallwidth are hardly perceptible optically and only disrupt vision throughthe pane 100 a little, which is of special importance for driving safetyin particular for use in motor vehicles.

The width b of the segments 10.1, 10.2, 10.3, 10.4 depends on the widthB of the electric heating layer 3 in a respective line 6 parallel to thebusbars 5.1,5.2. and is calculated by division of the width B by thenumber of segments. In FIG. 1, three parallel lines 6.1, 6.2, 6.3 aresketched in by way of example. The electric heating layer 3 has, alongthe line 6.1, for example, a width B of 98 cm. The width b₁ of thesegments 10.1, 10.2, 10.3, 10.4 is then ¼ B₁=24.5 cm. Since theseparating lines have a very small width of, for example, 100 μm, thiscan be ignored in the evaluation of the width b₁. Since the pane 100 isconfigured as a rectangle in this example, the width B₃ along the line6.3 is also 98 cm and the width b₃ is also 24.5 cm.

The width B₂ of the electric heating layer 3 along a line 6.2 in theregion of the uncoated zone 8 is calculated by the addition B₂₁+B₂₂, inother words, the stretch along the line 6.2 in the uncoated zone 8 isnot part of the width B₂. Here, the width B₂ is, for example, 88 cm,such that the width b₂ of the segments 10.1, 10.2, 10.3, 10.4 is 22 cm.

FIG. 2 depicts a pane 100 according to the prior art. The first pane 1,the busbars 5.1, 5.2, the electric heating layer 3, as well as theuncoated zone 8 correspond to the pane 100 of FIG. 1. The pane 100according to the prior art has no separating lines and, as a result, nosegments that guide the current path 11 around the uncoated zone 8. Theheating power distribution of the pane 100 according to the prior art isvery inhomogeneous. Only a small current flows through the regions 12above and below the uncoated zone 8, and the pane 100 according to theprior art is only heated insignificantly in the regions 12.

FIG. 3 depicts a plan view of another exemplary embodiment of a pane 100according to the invention having an electric heating layer. The pane100 comprises a first pane 1 and a second pane 2, which are bonded toeach other via a thermoplastic intermediate layer 4. The pane 100 is,for example, a motor vehicle window and, in particular, the windshieldof an automobile. The first pane 1 is, for example, intended to face theinterior in the installed position. The first pane 1 and the second pane2 are made of soda lime glass. The thickness of the first pane 1 is, forexample, 1.6 mm and the thickness of the second pane 2 is 2.1 mm. Thethermoplastic intermediate layer 4 is made of polyvinyl butyral (PVB)and has a thickness of 0.76 mm. An electric heating layer 3 made of anelectrically conductive coating is applied on the interior-side surfaceIII of the first pane 1. The electric heating layer 3 is a layer systemthat contains, for example, three electrically conductive silver layersthat are separated from each other by dielectric layers. When a currentflows through the electric heating layer 3, it is heated due to itselectrical resistance and Joule heat development. The electric heatinglayer 3 can, consequently, be used for active heating of the pane 100.

The electric heating layer 3 extends, for example, over the entiresurface Ill of the first pane 1 minus a circumferential frame-shapeduncoated region with a width of 8 mm. The uncoated region is used forthe electrical insulation between the current-carrying electric heatinglayer 3 and the motor vehicle body. The uncoated region is hermeticallysealed by gluing to the intermediate layer 4 to protect the electricheating layer 3 against damage and corrosion.

For the electrical contacting of the electric heating layer 3, in eachcase, a first busbar 5.1 is arranged in the lower edge region andanother, second busbar 5.2 is arranged in the upper edge region on theelectric heating layer 3. The busbars 5.1, 5.2 contain, for example,silver particles and were applied by screen printing and then fired. Thelength of the busbars 5.1, 5.2 corresponds to approximately thedimension of the electric heating layer 3.

When an electric voltage is applied to the busbars 5.1 and 5.2, auniform current flows through the electric heating layer 3 between thebusbars 5.1, 5.2. A feed line 7 is arranged approximately centrally oneach busbar 5.1, 5.2. The feed line 7 is a foil conductor known per se.The feed line 7 is electrically conductively connected to the busbar5.1, 5.2 via a contact surface, for example, by means of a solderingcompound, an electrically conductive adhesive, or by simple placementand application of pressure inside the pane 100. The foil conductorcontains, for example, a tinned copper foil with a width of 10 mm and athickness of 0.3 mm. The busbars 5.1, 5.2 are connected via theelectrical feed lines 7 via connecting cable 13 to a voltage source 14,which provides a customary onboard voltage for motor vehicles,preferably from 12 V to 15 V and, for example, roughly 14 V.Alternatively, the voltage source 14 can even have higher voltages, forexample, from 35 V to 45 V, and in particular 42 V.

An uncoated zone 8 is arranged in the pane 100 roughly centrallyrelative to the width of the pane. The uncoated zone 8 has noelectrically conductive material of the electric heating layer 3. Here,the uncoated zone 8 is, for example, completely surrounded by theelectric heating layer 3. Alternatively, the uncoated zone 8 can bearranged at the edge of the electric heating layer 3. The area of theuncoated zone 8 is, for example, 1.5 dm². The length of the uncoatedzone 8 is, for example, 10 cm. Here, the term “length” means thedimension in the direction that runs in the direction of the currentpath through the pane, i.e., in the direction of the shortest connectingline between the busbars 5.1, 5.2. In the example of the motor vehiclewindow of FIG. 1, the length of the uncoated zone 8 is arranged in thevertical direction and the width in the horizontal direction, parallelto the busbars 5.1, 5.2. The uncoated zone 8 is adjacent the busbar 5.3on its upper end.

The busbars 5.1, 5.2, 5.3 have, in the example depicted, a constantthickness of, for example, roughly 10 μm and a constant specificresistance of, for example, 2.3 μohm·cm.

Here, the electric heating layer 3 has n=7 separating lines 9.1-9.7. Inthe region of the separating lines 9.1-9.7, the electric heating layer 3is electrically interrupted. The separating lines 9.1-9.7 are arrangedin strip form around the uncoated zone 8 and form 8 segments 10.1-10.8in the electric heating layer 3. After application of a voltage on thebusbars 5.1, 5.2, the electrical current is guided around the uncoatedzone 8 through the segments 10.1-10.8 in the electric heating layer 3.

The separating lines 9.1-9.7 have a width of, for example, only 100 μmand are, for example, introduced into the electric heating layer 3 bylaser patterning. Separating lines 9.1-9.7 with such a small width arehardly perceptible optically and only disrupt vision through the pane100 a little, which is of special importance for driving safety inparticular for use in motor vehicles.

The width b of the segments 10.1-10.8 depends on the width B of theelectric heating layer 3 in a respective line 6 parallel to the busbars5.1, 5.2. The width b of the segments 10.1-10.8 is calculated bydivision of the width B by the number of segments. In FIG. 2, threeparallel lines 6.1, 6.2, 6.3 are sketched in by way of example. Theelectric heating layer 3 has, along the line 6.1, for example, a widthB₁. The width b₁ of the segments 10.1-10.8 is then ⅛ B₁. Since theelectric heating layer 3 is configured as a trapezoid in this example,the width b₃ of the segments 10.1-10.8 along the line 6.3 is ⅛ B₃. Thewidth B₂ along the line 6.2 is, as stated in FIG. 1, understood to bewithout the width of the uncoated zone 8.

FIG. 4 depicts a plan view of another embodiment of a pane 100 accordingto the invention. The first pane 1, the busbars 5.1, 5.2, and theelectric heating layer 3 correspond to the pane 100 of FIG. 1. Anuncoated zone 8 is arranged, by way of example, in the upper left cornerof the pane 100.

Here, the electric heating layer 3 has n=1 separating line 9.1. In theregion of the separating line 9.1, which subdivides the electric heatinglayer into two segments 10.1, 10.2. The electric heating layer 3 has,along the line 6.1, for example, a width B₁ of 98 cm. The width b₁ ofthe segments 10.1, 10.2 is then ½ B₁=49 cm.

The width B₂ of the electric heating layer 3 along a line 6.2 in theregion of the uncoated zone 8 is, for example, 93 cm, such that thewidth b₂ of the segments 10.1, 10.2 is 46.5 cm.

FIG. 5 depicts a plan view of another embodiment of a pane 100 accordingto the invention. The first pane 1, the busbars 5.1, 5.2, and theelectric heating layer 3 correspond to the pane 100 of FIG. 1. Anuncoated zone 8 is arranged, by way of example, in the upper left cornerof the pane 100. The uncoated zone 8 has, for example, a rectangularshape with one rounded corner. Rounded corners in the electric heatinglayer 3 are particularly advantageous since, by this means, local heatconcentrations, so-called hotspots, are avoided.

Here, the electric heating layer 3 has n=1 separating line 9.1. In theregion of the separating line 9.1, which subdivides the electric heatinglayer into two segments 10.1, 10.2. The electric heating layer 3 has,along the line 6.1, for example, a width B₁ of 98 cm. The width b₁ ofthe segments 10.1, 10.2 is then ½ B₁ =49 cm.

The width B₂ of the electric heating layer 3 along a line 6.2 in theregion of the uncoated zone 8 is, for example, 93 cm, such that thewidth b₂ of the segments 10.1, 10.2 is 46.5 cm.

FIG. 6 depicts a flowchart of an exemplary embodiment of the methodaccording to the invention for producing a pane 100 having an electricheating layer 3 using the example of a composite glass pane.

The pane 100 according to the invention in accordance with FIGS. 1 and3-5 has improved heating properties, such as more homogeneous heatingpower distribution and more homogeneous temperature distribution, inparticular in the critical region 12 below the uncoated zone 8. The viewthrough the pane is only minimally impaired due to the low width of thelaser-patterned separating lines 9 and satisfies the requirements for amotor vehicle glazing.

This result was unexpected and surprising for the person skilled in theart.

LIST OF REFERENCE CHARACTERS

-   (1) first pane-   (2) second pane-   (3) electric heating layer, electrically conductive coating,-   (4) thermoplastic intermediate layer-   (5.1), (5.2) busbar-   (6.1), (6.2), (6.3) line-   (7) feed line-   (8) uncoated region, communication window-   (9.1), (9.2), (9.3), (9.4), (9.5), (9.6), (9.7) separating line,    separating zone-   (10.1), (10.2), (10.3), (10.4), (10.5), (10.6), (10.7), (10.8)    segment-   (11) current path-   (12) region-   (13) connecting cable-   (14) voltage source-   (100) pane, electrically heatable pane-   (III) surface of the first pane 1-   b, b₁, b₂, b₃ width of the segments 10.1-10.8-   B, B₁, B₂, B₃ width of the electric heating layer 3-   d width of the separation line 9.1-9.7

What is claimed is:
 1. A pane having an electric heating layer,comprising: a pane with a surface; at least one electric heating layerthat is applied at least on part of the surface and includes at leastone uncoated zone in a corner of the surface; at least two busbarsprovided for connection to a voltage source, at least two busbars beingconnected to the electric heating layer such that a current path for aheating current is formed between the at least two busbars; and at leastone separating line that electrically subdivides the electric heatinglayer into at least two segments, wherein there is only one more of theat least two segments than the at least one separating line; wherein theat least two segments are arranged in strip form such that the currentpath for the heating current is guided curving away from the at leastone uncoated zone, wherein, for each busbar of the at least two busbars,the at least two segments have equal widths at that busbar.
 2. The paneaccording to claim 1, wherein the at least one electric heating layerhas three separating lines.
 3. The pane according to claim 1, whereinthe at least one electric heating layer has at least seven separatinglines and no more than twenty-five separating lines.
 4. The paneaccording to claim 1, wherein a width of each separating line is from 30μm to 200 μm at a given busbar.
 5. The pane according to claim 1,wherein a width of each separating line is from 70 μm to 140 μm at agiven busbar.
 6. The pane according to claim 1, wherein an area of theuncoated zone is from 0.5 dm² to 15 dm².
 7. The pane according to claim1, wherein an area of the uncoated zone is from 2 dm² to 8 dm².
 8. Thepane according to claim 1, wherein at least one of the at least twobusbars is implemented as fired printing paste.
 9. The pane according toclaim 8, wherein the fired printing paste contains at least one ofmetallic particles, metal particles, and carbon particles.
 10. The paneaccording to claim 8, wherein the fired printing paste has a specificresistance from 0.8 μohm·cm to 7.0 μohm·cm.
 11. The pane according toclaim 8, wherein the fired printing paste has a maximum width from 4 mmto 30 mm.
 12. The pane according to claim 1, wherein the at least twobusbars are arranged on one or more of a region of the electric heatinglayer and the surface of the pane that is areally bonded to a secondpane via a thermoplastic intermediate layer.
 13. The pane according toclaim 1, wherein the pane contains glass.
 14. The pane according toclaim 1, wherein the pane contains flat glass, float glass, quartzglass, borosilicate glass, or soda lime glass.
 15. The pane according toclaim 1, wherein the pane contains a polymer.
 16. The pane according toclaim 1, wherein the pane contains one or more of polyethylene,polypropylene, polycarbonate, and polymethyl methacrylate.
 17. The paneaccording to claim 1, wherein the electric heating layer is atransparent, electrically conductive coating.
 18. The pane according toclaim 17, wherein the electric heating layer has a sheet resistance from0.4 ohm/square to 10 ohm/square.
 19. The pane according to claim 18,wherein the electric heating layer contains silver, indium tin oxide,fluorine-doped tin oxide, or aluminum-doped zinc oxide.
 20. A method forproducing a pane having an electric heating layer, comprising: applyingan electric heating layer having an uncoated zone onto a surface of apane, such that the uncoated zone is in a corner of the surface;connecting at least two busbars to the electric heating layer, the atleast two busbars being configured for connection to a voltage sourceand being parallel to each other such that a current path for a heatingcurrent is formed between the busbars; and introducing at least oneseparating line that electrically subdivides the electric heating layerinto at least two segments, wherein there is only one more of the atleast two segments than the at least one separating line, wherein eachof the segments are arranged at least partially in strip form past theuncoated zone such that the current path for the heating current isguided curving away from the uncoated zone, and wherein, for each busbarof the at least two busbars, the at least two segments have equal widthsat that busbar.
 21. The method according to claim 20, whereinintroducing at least one separating line includes laser patterning.